The present invention relates to a brake force generator having a force input element, which is connectable or connected to a brake pedal and displaceable in a base housing of the brake force generator, a master cylinder, in which a primary piston is displaceably guided, wherein the primary piston with the master cylinder delimits a primary pressure chamber for generating a hydraulic brake pressure, a pedal counterforce simulating device connectable to the force input element, a pedal actuation detecting device for detecting a pedal actuation, and an actuating force generating device for generating an actuating force that acts upon the primary piston.
In currently conventional brake systems, the hydraulic brake pressure required for acting upon the wheel brake of the vehicle is generated predominantly by means of a master cylinder. For this purpose, it is necessary to initiate an actuating force upon the said master cylinder that is generated in response to an actuation of the brake pedal by the vehicle driver. For improved actuating comfort, the actual brake pedal force is usually increased by a predetermined percentage by means of a brake booster so that the necessary brake pedal actuating forces for a desired vehicle deceleration may be kept low enough to allow each driver to brake the vehicle adequately without exertion. Such a brake system with brake booster is known for example from DE 44 05 092, and corresponding U.S. Pat. No. 5,493,946, both of which are incorporated by reference herein.
A disadvantageous effect of these brake systems is that the driver by virtue of his actuating action at the brake pedal always influences the hydraulic pressure at the wheel brakes. So long as this assists the braking situation, it is not a problem. However, as soon as the driver reacts incorrectly to the actual braking situation, for example by adjusting too much or too little brake pressure, the braking performance, in particular the braking distance and the stability of the vehicle may be adversely affected, which in the worst-case scenario may lead to an accident.
Modern vehicle control systems (ABS, ESP, TC etc.) are now able to determine from the instantaneous driving state of the vehicle the optimum braking power requirement within the physical limits and hence to optimize a braking operation. A prerequisite of this is, however, to prevent the previously mentioned direct influence of the driver on the brake pressure. Furthermore, it has meanwhile begun to be regarded as unacceptable that the driver senses the action of the vehicle control system at the brake pedal, for example a repeated shaking at the brake pedal upon activation of the ABS.
In order to meet these requirements associated with vehicle control systems, in modern brake systems the brake pedal is already uncoupled from the brake force generation, in which case the brake pedal actuation is used merely to communicate the deceleration request of the driver. The actual brake force generation, for example for actuating the master cylinder, is then effected by means of a separate brake force generator, namely solely on the basis of control data of an electronic control unit. It is therefore possible to check in advance whether or not, for example, the desired vehicle deceleration would exceed the instantaneously effective physical limits in respect of braking distance and vehicle stability that are determined by the vehicle control systems (ABS, ESP, TC etc.). At the same time, the control unit may of course also compensate an inadequate deceleration adjusted by the driver in order to minimize the stopping distance in emergency situations through adjustment of a higher brake pressure. Such a system is described for example in the generic background art according to EP 1 070 006. It has however emerged that such brake systems are relatively cost-intensive to manufacture and entail a considerable equipment outlay in order to guarantee reliable brake operation also in the event of failure of the brake force generating means.